Abstract

While control of intracellular pathogens, such as the protozoan Leishmania, is dependent on the generation of type-1 immune responses, the role of T helper 2 cytokines in the disease process is more controversial. Traditionally these cytokines were perceived as counter-regulating type-1 responses and promoting disease exacerbation. Nevertheless a substantial body of evidence now exists suggesting that the development of effective type-1 immunity can involve the significant involvement of the Th2 cytokines IL-4 and IL-13. This article reviews, using Leishmania species in particular, the circumstances under which these cytokines can promote protective type-1 immunity.